21 weeks pregnant
At 21 weeks you are in the second trimester, and your baby measures about 27 cm from head to heel and weighs about 360 g, roughly the length of a carrot. The 20-week antenatal visit falls between now and 22+6, and public hospital antenatal classes for 28 to 34 weeks fill now, so book this week.
Weighs about 360 g, like a full can of soft drink. Averages from standard growth tables; your scan gives your baby's own numbers.
Your baby at 21 weeks
Movements become stronger and more regular. Curled in the fetal position and filling out with fat; the eyes open from about week 26.
How you might feel
Movements become stronger and more regular, and stretch marks, heartburn and a stuffy nose are common.
Book antenatal classes and think about childcare waitlists.
Call the maternity unit today for bleeding, fluid loss, a severe headache or vision changes. 13 HEALTH (13 43 25 84) in Queensland; 000 in an emergency.
What's due this week in Australia
Whooping cough (pertussis) vaccine
Free under the National Immunisation Program in every pregnancy.
20-week antenatal visit
Review of the morphology scan, blood pressure, the first fundal-height measurement and a chat about the baby’s movements.
Book antenatal classes and a hospital tour
Public hospitals run free or low-cost childbirth, breastfeeding and early-parenting classes, in person or online.
Put your name on childcare waitlists
If you plan to use childcare in the first year, many centres have waitlists of 6–12 months.
Coming up: 24–25-week antenatal visit (first pregnancy)
Blood pressure, fundal height, the baby’s movements, and the request forms for the glucose test and 28-week bloods.
Coming up: Gestational diabetes test (OGTT)
A fasting 75 g oral glucose tolerance test at a pathology collection centre: a fasting blood sample, the drink, then samples at 1 and 2 hours.
Checklist for the week
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Questions about 21 weeks
How many months is 21 weeks pregnant?
About five months.
What trimester is 21 weeks?
Week 21 is in the second trimester. In the Australian guidelines Hello Bub follows, the first trimester runs to 13 weeks, the second from 14 to 27 and the third from 28 weeks.
When should I book antenatal classes in Australia?
Book now for classes held at 28 to 34 weeks. Public hospital classes are free or low cost and fill quickly; private and online courses are the alternative.
Written by the Hello Bub team; medical schedule follows the Australian Pregnancy Care Guidelines; last reviewed 3 November 2026.